The present invention generally relates to lubrication systems. More particularly, the present invention relates to a viscous pumping system for lubricating a bearing that supports a shaft.
Lubrication systems are used in a variety of applications to lubricate bearings. Many machines, such as mills, pumps, and engines, include bearings that require lubrication to function properly. If the bearings supporting a machine are not lubricated properly, continued operation of the machine may cause the bearings to seize, thereby damaging the machine.
One example of a machine requiring a lubrication system is a variable capacity compressor. This type of compressor is used when it is desirable to vary the compressor output, such as in refrigeration, air conditioning, and heat pump systems, among others. Modulation between two stages allows large gains in efficiency while normally providing reduced sound, improved reliability, and improved creature comforts, including better de-humidification and warmer air in heat pump mode.
The efficiency gains resulting from a compressor with capacity modulation are beneficial in a variety of commercial applications. For example, most residential refrigerators currently utilize a single capacity compressor and cycle the compressor on and off to maintain a certain temperature within the cabinet of the refrigerator. During normal operation, the temperature in the cabinet of the refrigerator increases due to the warmer ambient air surrounding the refrigerator. The cabinet temperature also rises when the refrigerator door is opened or a load of perishables having a temperature greater than that of the cabinet is introduced to the refrigerator. If the temperature exceeds a preset limit, the compressor is activated to cool the cabinet of the refrigerator. To account for the higher load conditions when the door is opened or perishables are introduced, the cooling capacity of the compressor is necessarily greater than the minimum required to maintain a particular temperature in the ambient conditions. With this design, the compressor undergoes multiple starts and stops to respond to varying load conditions. The high number of starts and stops will shorten the life of the compressor. Additionally, operating the compressor at full capacity during periods of minimal load is inefficient.
In a reciprocating piston type of variable capacity compressor, the stroke length of one or more of the reciprocating pistons is varied to change the volumetric capacity of the cylinder. The piston attains a full stroke length when the bearing-supported shaft rotates in the forward direction and attains a reduced stroke length when the shaft rotates in the reverse direction. Such an approach requires a motor or other drive system with a reversible shaft, i.e., one capable of rotating in a forward and a reverse direction.
Most lubrication systems for compressors are designed to lubricate a shaft that rotates in one direction only. A common lubrication system consists of a single helical groove that traverses the shaft to pump a lubricant from a reservoir in the compressor housing to the upper portion of the bearing when the shaft rotates in one direction. If the rotation of the shaft were reversed, however, these lubrication systems would draw lubricant out of the bearing, potentially causing the bearing to seize and/or damaging the compressor.
Lubrication systems that are known to the inventor and are designed to provide lubrication for both directions of shaft rotation also do not offer complete protection against seizure. Such a system typically consists of opposing helical grooves traversing the shaft. Lubricant is provided to the grooves in various manners. When the shaft rotates in the forward direction, the trailing edge of the first helical groove has a positive effect as it pumps lubricant to the bearing, but the trailing edge of the second, opposing helical groove has a negative effect as it simultaneously pumps lubricant out of the bearing. When the shaft rotates in the reverse direction, the trailing edge of the second helical groove has a positive effect as it pumps lubricant to the bearing, but the trailing edge of the first, opposing helical groove has a negative effect as it simultaneously pumps lubricant out of the bearing. Because the system pumps lubricant out of the bearing at the same time it is pumping lubricant to the bearing, the system is inefficient and results in increased wear on the compressor components, increased warranty costs for the components, and potential bearing seizure and compressor damage.
In light of the foregoing, there is a need for a system that efficiently lubricates the bearing of a reversible shaft irrespective of the direction of rotation of the shaft.
Accordingly, the present invention is directed to a viscous pumping system for lubricating a bearing that supports a reversible shaft. The pumping system provides lubrication to the bearing irrespective of the direction of rotation of the shaft. Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
In accordance with achieving the objects and the purpose of the invention, as embodied and broadly described herein, the invention is directed to a viscous pumping system for lubricating a bearing. The system comprises a reservoir configured to store a lubricant, a housing connected to the reservoir and mounting the bearing, and a shaft disposed in the housing and supported by the bearing. The shaft is rotatable in both a forward and a reverse direction. The shaft has at least two helical grooves that are configured to sufficiently lubricate the bearing irrespective of whether the shaft rotates in the forward direction or the reverse direction.
In another aspect, the invention is directed to a viscous pumping system for lubricating a bearing via specifically configured helical groove edges. The system comprises a reservoir designed to store a lubricant, a housing connected to the reservoir and mounting the bearing, and a shaft disposed in the housing and supported by the bearing. The shaft is rotatable in both a forward and a reverse direction and has two helical grooves. The first helical groove has a first edge configured to pump lubricant contained in the reservoir to the bearing when the shaft rotates in the forward direction and a second edge configured to substantially avoid pumping lubricant away from the bearing when the shaft rotates in the reverse direction. The second helical groove has a second edge configured to substantially avoid pumping lubricant away from the bearing when the shaft rotates in the forward direction and a first edge configured to pump lubricant contained in the reservoir to the bearing when the shaft rotates in the reverse direction.
In another aspect, the invention is directed to a viscous pumping system for lubricating a bearing via a groove structure in combination with a lubricant pickup system. The system comprises a reservoir designed to store a lubricant, a housing connected to the reservoir and mounting the bearing, and a shaft disposed in the housing and supported by the bearing. The shaft is rotatable in a forward direction and a reverse direction and has a first helical groove and a second helical groove emanating from a groove origin. Additionally, the system includes a lubricant pickup system disposed within the shaft and configured to transport the lubricant from a lubricant entrance located at the reservoir, up the shaft, and out of a lubricant exit located at the groove origin. In combination, the pickup system, the first helical groove, and the second helical groove are configured to sufficiently lubricate the bearing when the shaft rotates in both the forward direction and the reverse direction.
In yet another aspect, the invention is directed to a variable capacity compressor. This compressor comprises a block that defines a lubricant reservoir and a cylinder having an associated compression chamber and an associated piston. The compressor further comprises a bearing disposed in the block and a shaft that is supported by the bearing and rotatable in both the forward and the reverse direction. The shaft is connected to the piston to provide a first stroke length when the shaft rotates in the forward direction and a second stroke length when the shaft rotates in the reverse direction. The first stroke length differs from the second stroke length. The shaft may have two helical grooves configured to pump lubricant contained in the reservoir from the groove origin to the bearing when the shaft rotates in the forward direction and when it rotates in the reverse direction. In one aspect of the compressor system, the edges of the helical grooves are configured to pump sufficient lubricant from a groove origin to the bearing irrespective of the direction of rotation of the shaft. In another aspect of the compressor system, the combination of a lubricant pickup system and configured helical groove edges is operable to sufficiently lubricate the bearing irrespective of the direction of rotation of the shaft.
In each aspect of the invention, the configuration of the groove edges is either entirely or partially responsible for the pumping effect regardless of the direction of rotation of the shaft. In a certain embodiment, if the shaft rotates in a forward direction, for example, one of the two grooves, the xe2x80x9cactivexe2x80x9d groove for the forward rotation, will pump lubricant to the bearing. Meanwhile, the second, xe2x80x9cpassivexe2x80x9d groove for the forward direction substantially avoids pumping lubricant away from the bearing. When the direction of rotation of the shaft is reversed, what was the active groove in the forward direction becomes the passive groove in the reverse direction, and the formerly passive groove becomes active. In certain other embodiments, the grooves are not xe2x80x9cactivexe2x80x9d and xe2x80x9cpassive.xe2x80x9d Rather, due to the configuration of the lubricant pickup system, in a particular direction of rotation of the shaft, one of the two grooves, the xe2x80x9cpositivexe2x80x9d groove, pumps lubricant to the bearing. The other, xe2x80x9cnegativexe2x80x9d groove pumps a minimal amount of lubricant out of the bearing in comparison to the amount of lubricant pumped to the bearing by the combination of the lubricant pickup system and the xe2x80x9cpositivexe2x80x9d groove. In the opposite direction of rotation of the shaft, the roles of the grooves reverse so that the formerly xe2x80x9cnegativexe2x80x9d groove pumps lubricant to the bearing and the formerly xe2x80x9cpositivexe2x80x9d groove pumps a relatively minimal amount of lubricant out of the bearing.
In all embodiments of the invention, the net result is that the bearing is sufficiently lubricated regardless of the direction of rotation of the shaft. In one embodiment, the tapered grooves alone are responsible; in another embodiment, the grooves in combination with a specially configured lubricant pickup system are responsible. One such lubricant pickup system is configured so that centrifugal forces suction lubricant out of the reservoir, up the shaft, into the lubricant pickup exit and out of the groove origin.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.